In this lecture you will:
|Type of waves||Main interaction||SOUND||LIGHT (EMS)|
|INTERFERENCE||Run into each other||acoustics (loud/soft)||holograms (bright/dark)|
|REFLECTION||Hit and bounce off surfaces||acoustics: echoes and reverberations||mirrors, colors, shiny and matte|
|REFRACTION||Enter clear materials and bends||rumble of thunderstorms||lenses, diamonds, rainbows|
|DIFFRACTION||Bend around solid or little slit||how we hear around a post||slits, rainbow effect on CD or DVD|
|When waves enter transparent or translucent
materials and bends
"Refraction is the bending of waves when they enter a medium where their speed is different. Refraction is not so important a phenomenon with sound as it is with light where it is responsible for image formation by lenses, the eye, cameras, etc. But bending of sound waves does occur and is an interesting phenomena in sound"
An example is of rolling wheels on a cart. When the leading wheels hit the grass which has more friction and drag, the leading wheel is slowed down first compared with the other wheel. This yanks the whole wagon toward the "normal".
Try this: if you are on roller skates, roll off the sidewalk with your right skate hitting the grass first and see if that pulls you around to the right.
|"Thunder is the acoustic shock wave resulting
from the extreme heat generated by a lightning flash. Lightning can be
as hot as 54,000°F (30,000°C), a temperature that is five times
the surface of the sun! When lightning occurs, it heats the air surrounding
its channel to that same incredible temperature in a fraction of a second.
Like all gases, when air molecules are
heated, they expand. The faster they are heated, the faster their rate
of expansion. But when air is heated to 54,000°F in a fraction of a
second, a phenomenon known as "explosive expansion" occurs. This is where
air expands so rapidly that it compresses the air in front of it, forming
a shock wave similar to a sonic boom. Exploding
fireworks produce a similar result."
|A prism splits light into component wave lengths by sending white light thru two REFRACTION events the second at an angle and the "double" bend splits white light.|
|"Rainbows can be observed whenever there
are water drops in the air and sunlight shining from behind at a low
altitude angle. The most spectacular rainbow displays happen when half
of the sky is still dark with raining clouds and the observer is at a spot
with clear sky in the direction of the Sun. The result is a luminous rainbow
that contrasts with the darkened background."
A raindrop breaks white light up by an
initial refraction event and then reflects the light against the inside
of the raindrop so the light bounces out the front of the drop where it
bends again as it exits the raindrop. This is two refractions and
one reflection. To see a rainbow, the Sun needs to be at about 23o angle
above the horizon. Stand with your back to the sun to see the rainbow.
In water droplets the light experiences TOTAL internal reflection so the light bounces back out at the observer.
|This is a double rainbow.
Notice how the area inside the inner rainbow is LIGHT, this is due to the raindrops refracting the light so it goes toward the CENTER. Also notice that the shortest waves, blue, bend the most and appear on the inner aspect of the inner rainbow and red, the longest wavelength is on the outside. The outer rainbow is reversed so that red is on the inside, blue on the outside.
|"98% of a diamond’s fire and brilliance is created by the quality of its cut and proportions, not its clarity, color, or size. Its proportions, polish, and the symmetry of its facets are primary to its radiance. None of the other factors, color, clarity, or carat weight, have more of a dramatic effect on a diamonds beauty than the cut... Subtle and minute structural differences of half a millimeter or less will determine whether a diamond will be full of Brilliance or dull and lifeless." cite||
Diamonds in the rough
|It is both the prism like effect of two
refractions and the internal reflections that make diamonds sparkle. Diamonds
are good candidates because they have such a high index of refraction.
"Bright diamonds return lots of light from the surroundings back to a 'face up' an observer. If light from above leaks out the back of a diamond, naturally it has less brightness. But light that enters and leaves in the face up direction is wasted because your head blocks the lights. Diamonds that are too deep or very shallow do this -they have areas that act like a mirror back to the viewer; they return less light and so they have less brightness. Fire or dispersed light appears as flashes of rainbow colors."
|Water both REFRACTS and REFLECTS light.
When the moon (or Sun) is at 48.75 (OK, 49o) degrees above the horizon a point called the "critical angle" is seen as a "path" of moon on water, or, a path of the Sun is seen.
Early in the morning and late at night
the angle is at around 49o all the Sun is reflected. One reason drivers
going east in the morning and west after work find the sun so blinding,
the situation that drivers from the western suburbs have going to work
in Milwaukee is because early and late the Sun is totally reflected right
into their eyes.
|loud and soft areas of sound in concerts||sound interference|
|bright or dim areas lined up in a row on a surface||light interference|
|holograms||light interference using lasers|
|colors||light reflection and absorption|
|shiny or matte||light reflection and interference|
|soap bubbles and oil spill rainbows||light reflection and interference|
|the rumble of thunder||sound refraction|
|prism rainbow||light refraction|
|rainbows||light refraction and reflection|
|diamonds twinkle||light refraction and reflection|
|blinding early morning light||reflection less than critical angle 50o|